Transfer Function for a negative feedback loop

Discussion in 'Math' started by smarch, Nov 20, 2010.

  1. smarch

    Thread Starter Active Member

    Mar 14, 2009
    52
    0
    Hi guys would appreciate the help.
    I am having trouble with this question.

    From the JPEG I have a attached:

    Determine the equivalent T.F. G(s) in form of G(s) = \frac{p}{qs+r}, where p, q, r are constants.

    I have tried working it out, but got into a mess. Help please, how do you do it?

    Thanks
     
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    Last edited: Nov 20, 2010
  2. guitarguy12387

    Active Member

    Apr 10, 2008
    359
    12
    Can ya post your work?

    In general, for a closed loop system, you have:

    TF = (direct path gain)/(1 - sum of loop gain)

    From there it is just algebra to get into the right form
     
  3. smarch

    Thread Starter Active Member

    Mar 14, 2009
    52
    0
    I come to :

    C(s) = R(s).(10/3s - 5) - C(s)(40/3s - 20)

    Am I on the right track?
    I have limited notes on this and have tried to follow it as they are in the notes, but it is quite a different problem to that one.
     
  4. guitarguy12387

    Active Member

    Apr 10, 2008
    359
    12
    Yeah that looks about right i think.

    Now just solve for C(s)/R(s)
     
  5. smarch

    Thread Starter Active Member

    Mar 14, 2009
    52
    0
    How do you complete it all the way through to get G(s) = \frac{p}{qs+r}
     
  6. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    First read here:http://en.wikipedia.org/wiki/Control_theory in the section Closed Loop Tranfer Funtion. In your case you have C=5, P=\frac{2}{3s}-1 and F=-4;

    Try to calculate the Transfer Function H(s).

    Post it and we will discuss more.
     
  7. krishna chaitanya

    New Member

    Nov 8, 2010
    5
    0
    TF = (direct path gain)/(1 - sum of loop gain)..

    it will give ans for this...
     
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